Cratonic sequence

They are geologic evidence of relative sea level rising and then falling (transgressing and regressing), thereby depositing varying layers of sediment onto the craton, now expressed as sedimentary rock.

The top and bottom edges of a sequence are each bounded by craton-wide unconformities (time gaps in the rock record).

[3] This elevated lithosphere displaces seawater onto the continents; conversely, when spreading rates decline, the ridges subside, and the seas drain from the cratons.

For North America, from oldest to youngest, they are the Sauk, Tippecanoe, Kaskaskia, Absaroka, Zuñi, and Tejas sequences.

Attempts to identify equivalent cratonic sequences on other continents have met with only limited success, suggesting that eustasy (total global sea-level change) is unlikely to be the sole responsible mechanism.

The Western Interior Seaway , illustrated at 95 million years ago, was a result of transgression onto the North American continent during the mid- Cretaceous period. Sediment deposited by this seaway is represented in the rock record by the Zuñi sequence .